Re: multip register_uprobe

[Wenji Huang <wenji.huang@oracle.com>]

Hi, Jim

   Got it, I also tried the several cases by changing hander/vaddr, but 
using same probe. Also works, no problem.

Thanks,
Wenji

Jim Keniston wrote:

>On Fri, 2007-07-06 at 09:37 -0700, Jim Keniston wrote:
>  
>
>>On Fri, 2007-07-06 at 18:05 +0530, Srikar Dronamraju wrote:
>>    
>>
>>>Hi Wenji,
>>>
>>>
>>>      
>>>
>>>>  I am creating some test scripts based on sarikar's framework.
>>>> 
>>>>  There is one problem about register multiple times.
>>>>      .................
>>>>       probes->vaddr = vaddr;
>>>>       probes->pid = pid;
>>>>       probes->handler = handler;
>>>>       for (i=0; i < 3; i++) {
>>>>            ret = register_uprobe(probes);
>>>>            if (ret!=0)  //of course, the first time should succeed and 
>>>>will failed in second time, ret = -16
>>>>              {
>>>>I tried several possibilities:
>>>>        
>>>>
>...
>  
>
>>>>                * return 0; //RESULT: same as above
>>>>        
>>>>
>>The above approach should work, assuming your cleanup function
>>unregisters the probe.
>>
>>You have found a bug.  Thanks!  I will post a fix shortly.
>>
>>    
>>
>
>Attached are a patch with the fix and a module (wenji3x.c) that
>demonstrates the bug (or fix).  This patch applies atop the May 26 (GMT)
>uprobes patch set.
>
>Thanks again.
>Jim
>  
>
>------------------------------------------------------------------------
>
>
>If register_uprobe() or register_uretprobe() fails while attempting to
>register a probe on a process that already has one or more u[ret]probes
>in place, subsequent uprobes activity on that process (probe hits,
>register/unregister attempts) may hang.  Here's a fix.
>
>---
>
> kernel/uprobes.c |    4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
>diff -puN kernel/uprobes.c~reused-probe-fix kernel/uprobes.c
>--- linux-2.6.21-rc6/kernel/uprobes.c~reused-probe-fix	2007-07-06 09:16:49.000000000 -0700
>+++ linux-2.6.21-rc6-jimk/kernel/uprobes.c	2007-07-06 09:18:56.000000000 -0700
>@@ -830,8 +830,10 @@ fail_uproc:
> 	if (uproc_is_new) {
> 		uprobe_free_process(uproc);
> 		mutex_unlock(&uproc_mutex);
>-	} else
>+	} else {
>+		up_write(&uproc->rwsem);
> 		uprobe_put_process(uproc);
>+	}
> 
> fail_tsk:
> 	put_task_struct(p);
>_
>  
>
>------------------------------------------------------------------------
>
>/* uprobe_example.c, modified to try to register the same probe 3 times */
>#include <linux/module.h>
>#include <linux/kernel.h>
>#include <linux/init.h>
>#include <linux/uprobes.h>
>
>/*
> * Usage: insmod wenji3x.ko pid=<pid> vaddr=<address> [verbose=0]
> * where <pid> identifies the probed process and <address> is the virtual
> * address of the probed instruction.
> *
> * insmod should report success (0) for the first registration attempt
> * and failure (-16 = EBUSY) for the second and third attempts.  The
> * probe should work.
> */
>
>static int pid = 0;
>module_param(pid, int, 0);
>MODULE_PARM_DESC(pid, "pid");
>
>static int verbose = 1;
>module_param(verbose, int, 0);
>MODULE_PARM_DESC(verbose, "verbose");
>
>static long vaddr = 0;
>module_param(vaddr, long, 0);
>MODULE_PARM_DESC(vaddr, "vaddr");
>
>static int nhits;
>static struct uprobe usp;
>
>static void uprobe_handler(struct uprobe *u, struct pt_regs *regs)
>{
>	nhits++;
>	if (verbose)
>		printk(KERN_INFO "Hit #%d on probepoint at %#lx\n",
>			nhits, u->vaddr);
>}
>
>int __init init_module(void)
>{
>	int ret, try, success = 0;
>	usp.pid = pid;
>	usp.vaddr = vaddr;
>	usp.handler = uprobe_handler;
>	printk(KERN_INFO "Registering uprobe on pid %d, vaddr %#lx\n",
>		usp.pid, usp.vaddr);
>	for (try = 1; try <= 3; try++) {
>		ret = register_uprobe(&usp);
>		printk(KERN_ERR "Try #%d: register_uprobe() returned %d\n",
>			try, ret);
>		if (ret == 0)
>			success++;
>	}
>	return (success ? 0 : ret);
>}
>
>void __exit cleanup_module(void)
>{
>	printk(KERN_INFO "Unregistering uprobe on pid %d, vaddr %#lx\n",
>		usp.pid, usp.vaddr);
>	printk(KERN_INFO "Probepoint was hit %d times\n", nhits);
>	unregister_uprobe(&usp);
>}
>MODULE_LICENSE("GPL");
>  
>